DESCRIPTION (Adapted from the abstract): Establishment of polarity in the egg can be viewed as the earliest step in embryonic patterning. Thus, differences in cell fate among the early cleavage cells are a consequence of asymmetric distributions of informational molecules in the egg cytoplasm before fertilization. The basis for such polarity is provided by localized maternal determinants in the form of protein or mRNA. While there is evidence for the existence of localized determinants in many systems, the localization process is still poorly understood. This research proposal addresses this problem by investigating the biochemical mechanisms underlying mRNA localization, using the frog Xenopus laevis as a model. The PI has purified and cloned an essential localization factor, identified other proteins that are potential localization factors, and defined these critical sequences within an RNA localization signal. The following specific aims are proposed: (1) characterization of VgRBP60, the essential localization factor; (2) investigation of the mechanism of mRNA localization; (3) analysis of other RNA-protein interactions mediating localization, and purification and characterization of other protein components of the localization machinery.